Electroacoustic transducer



kprfl 22 1947. BENlOFF 2,419,196

ELECTROACOUSTIG TRANSDUGER Filed May 3, 19%0 6 Sheets-Sheet 1 Ir \J 4- Ns i N s N N 5 5 N N 5 5 N v I 75' O /5 I61 com 15 CEMENTED TO BLOCK 5 aINVENTOR Hugo Ben/off ATTORNEY H"; EENIOFF 2,419,196

'ELECTHOAGOUST IC TRANS DUCER Filed May 3, 1940 s she ts-sheet 2INVENTOR 4590 Ben/015 April 22, 1947. H. BENIOFF 2,4193% ELECTROACOUSTIGTRANSDUCER Filed May a, 1940 s Sheets-Shed; s

INVENTOR p 22, 1947. H. BENIOFF 2,419,196

ELECTROACOUSTIC TRANSDUCER Filed May 3, 1940 6 Sheets-Sheet 4 FIG. 6

April 22, 1947. H. BENIOFF 2,419,196

ELECTROACOUSTIC TRANSDUCER Filed May 3, 1940 6 Shee ts-Sheet 5 INVENTORHu va Eembff BY A ril 22, "1947. H. BENIOFF 2,419,196

ELECTROAQOUSTI C TRANSDUCER Filed May 3, 1940 6 Sheets-Sheet 6 FIGSINVENTOR Patented ZAiMtb ELECTROACOUSTIC TRANSDUCER Hugo Beniofi", LaCanada, Calif., assignor, by

mesne assignments, to Submarine Signal Company, Boston, Mass, acorporation of Delaware Application May 3, 1940, Serial No. 333,157

17 Claims.

transducers. More particularly the present invention relates to a devicefor sending and receiving compressional Waves in a liquid medium andespecially for waves of supersonic frequency. Still more particularlythe present invention relates to a device of the type described which isoperated electromagnetically.

The various features and objects of the invention as well astheconstruction of the same will best be understood from the followingdescription taken in connection with the accompanying drawings in whichFig. 1 is a plan view of one modification of my invention with the coverin section, as indicated by the line l.I of Fig. 2; Fig. 2 is atransverse section taken along the line ill-ii in Fig. 1; Fig. 2a is anenlargement of a detail shown in Fig. 2; Fig. 3 is an end elevation ofthe device shown in Fig. 1 with the housing elements in section; Fig. 4is a transverse n1 section of a modification of the device shov. :1Figs. 1 to 3; Fig. 5 is a further modification of my invention, the lefthalf being a section taken along the line V--V in Fig. 6 and the righthalf being a plan view; Fig. 6 presents the same modifica'tion as thatshown in Fig. 5, the left half being a transverse midsection along theline .VI-VI in Fig. 5 and the right half being an elevation; Fig. 7shows a further modification of my invention, the left half being asection along the line VII-VII in Fig. 8 and the right half being a planview; and Fig. 8 is another illustration of the modification shown inFig. 7, the left half being a transverse midsection along the lineVIII-47111 in Fig. land the right half being an elevation.

As shown in Figs. 1 to 3 a diaphragm element l having a radiatingsurface 2 is provided with a thin annular flange 3 whereby it can beclamped by the bolts d between a ring member t and a cup-shaped flangedcover member t,

asuitable watertight gasket 1 being interposed so that a watertightenclosure is formed.

Upon the back face of the diaphragm l and within the enclosure formed bythe diaphragm and the cover member 6 there are mounted a plurality ofparallel elongated vibrators 8 of magnetic material which are held tothe member I by means of screws e which preferably are sunk into theface of the member 1, the resulting holes being filled by the plugs illto make a completely watertight joint and to provide the smoothradiating surface 2. At the upper ends of the vibrators 8 there isformed on each side a tongue or rib ll extending for the whole length ofthe member 8. These ribs H as seen in Fig. 2 are adapted to vibratevertically by flexing. Their vibration is, therefore, that of avibrating reed and they are hereinafter described as reeds.

The members 8 may be permanently magnetized but preferably aremagnetized by the direct current energized polarizing coils I2 which arewound around every alternate vibrating element 8. These coils areplacedin the space between the members 8 beneath the reeds II where they areheld down upon insulating rubber strips 83 between them and member I byend clamping strips 34 fastened to'the flange 3 by bolts 35.

The small spaces between adjacent reeds H, therefore, become magneticairgaps in which a. very high flux density can be obtained. Posi. tionedwithin the airgaps are the alternating current coils l3. These arepreferably made up of insulated thin 'ribbon conductors wound edgewise.The coils l3 may be mounted in the airgaps in any suitable manneravoiding elasticity in the mounting so far as possible. As shown, a pairof end plates I4 and I5 are mounted by screws I1 and I! on the flange 3.To the members It and I5 there is secured by the screws 58 a plate l9having a, plurality of parallel ribs 20 of non-magnetic material formedon the underside thereof. The ribs 20 are diminished in cross section at2| to athickness equal to the width of the conductors in coils I3 andthe coil windings are cemented'thereto. The end loops of the coils 13may be further-supported'by being cemented to blocks 36 (Fig. '3)secured in any suitable manner to the plate l9. The width of the airgapbetween the reeds H and the width of the coils l3 are so adjusted thatthe windings substantially fill the entire space without, however, atany point touching the reeds. Electrical conductors (not shown) formaking connections to the coils l2 and the coils [3 may be taken out ofthe casing through the liquid-tight stuffing tube 22.

The operation of the device is as, follows: The polarizing coils l2which may be connected in either series or parallel as desired, aresupplied with direct current, thereby magnetizing'the elements 8. Theseveral coils I! are wound in the same direction so that alternate northand 'south magnetic poles are formed as indicated, for example, by theletters N and S marked upon the reeds in Fig. 1 and upon the members 8in Fig. 2. The coils i3 which may also be connected either in series orin parallel as desired are excited with an alternating current. Sincethe-conductors of coils it are directly within the strong magnetic fieldexisting between the reeds II, there will be frequency of the reeds, thereeds will build up to a relatively large amplitude of vibration, butthe .coils I 3 will remain practically stationary. Moreover, the heightof the members 8 above the diaphragm member I is adjusted so that eachof 1 the members 8 together with that portion of the member I which isaifected by it, forms a onehalf wave length vibrational system at thenatural frequency of vibration of the reeds II which I adjacent reeds.

is preferably made to correspond to the signaling v frequency. Theflexural vibration of the reeds sets up stresses in the members 8 in thevertical direction as seen in Fig. 2, these stresses being of alternatecompression and elongation, whereby a vibration of the radiating surface2 is obtained.

It will be evident that a vibrational node will exist between theradiating surface 2 and the internal ends of the members 8. Thesupporting flange 3 is preferably placed as nearly as possible in theplane of the vibrational node. The ratio of the mass above thevibrational node to the mass below the vibrational node is adjusted toproduce the desired amplitude of vibration at the radiating surface 2.The radiating plate I is for this purpose made of a considerablethickness but not greater than one-fourth of the wave length ofcompressional waves in the material of which it is made at the signalingfrequency.

Viewed as a whole, the arrangement maybe regarded as a system of threemasses coupled to each other by elastic members. The mass of each reedII through the elasticity of the reed is coupled to the mass of itsmember 8, which in turn through its elasticity is coupled to thediaphragm mass I. Since the mass of the reeds is relatively small, thecoupling between the reeds and the half wavelength systems comprisingmembers 8 and diaphragm I is very loose. Therefore, the reeds can buildup to a relatively large vibrational amplitude. Moreover, the entiresystem will be sharply tuned with only one very prominent resonantfrequency which is determined .chiefly by the resonant frequency of thehalf wavelength through the space between one of the members 8 to theadjacent member and consequently it does not assist in the production ofmotion.

In the modification of Fig. 4 such leakage flux is almost entirelysuppressed by placing bipolar U-shaped permanent magnets '23.to 26 withtheir poles supported close to the ends of the members 8 and of samepolarity to the latter. A greater portion of the magnetic flux producedby the currents through the coils I2 is therefore forced to pass throughthe air gaps between the The permanent magnets 23 to 26 may besupportedfrom a plate 21 by means of screws 28. The plate 21 is mountedupon end plates 28 and .38 which may be similar to the plates I4 and I5in Fig. 2 and are likewise fas-' tened to the flange 3 of the diaphragmelement I. The alternating current coils I3 may in this case beconveniently mounted upon elongated members 3| fastened to the severalmagnets by means of the screws 82. In place of using the permanentmagnets 23 to 26 electromagnets could, of course, be employed, but thisis undesirable where the operating elements must be placed within awatertight housing since this sets up definite is well known in the art.if the dimensions ofthe radiating surface are made large compared to thewave length of compressional waves in the signaling medium, the devicewill have a beam pattern in which the greater portion of the transmittedenergy and the sensitivity pattern for reception will have theirgreatest magnitudes in the direction perpendicular to the radiatingsurface. In some cases it may be desirable to be able to radiate largeamounts of energy in all directions, especially in all directions in aplane.

is desirable.

Figs. 5 and 6 show a modification of my in I vention which provides sucha radiating surface.

In these figures the radiating element M having a cylindrical radiatingsurface 42 and provided plate establishes the dominant resonance of thesystem since the mass and total elasticity oi this element are muchgreater than that of the reed attached to it.

It will be understood, of course, that when the device is used forreceiving, the operation will be reversed. Compressional waves in themedium will vibrate the plate I and the members 8 which, in turn, willproduce fiexural vibrations of the reeds II. The consequent disturbanceof the magnetic field generates an electromotive force in the coils I3.

In the modification shown in Fig. 4, which presents a sectional viewlike that of Fig. 2, the general arrangement of the various elements aswell as their operation are substantially the same but increasedefliciency of operation is obtained. This results from an increase inthe flux density in the air gaps between adjacent reeds. In theconstruction shown in Fig. 2 most of the magnetic flux passes across theairgap between the reeds, but nevertheless a. considerable amount passesat its ends with a nodal flange 43 has mounted on its innerface aplurality of elongated vibrating elements 44, all mounted with theirlong dimensions parallel to the axis of'the cylinder and I projectingradially from the internal. surface of the member 4|. to the element 4|by means of screws 45 which are sunk into the outer face of the element8|, the resulting holes being made watertight by the plugs 46. Themembers 44 are similar to the members 8 in the modifications previouslydescribed and have formed along their sides near their inner endsthevibratory reeds 81. The elements 48 and the reeds 41 are magnetizedby direct current polarizing coils 48 forming magnetic poles asindicated by the letters N and S. The alternating current coils 49'arecemented to the arms or U-shaped non-magnetic metal channels 58 wherebythey are supported within the air gaps between adjacent reeds. Theelements 58 are held in position by being screwed by the screws 5| toupper and lower ring mem- For this purpose a radiating surfacewhich iscylindrical and which vibrates radially The elements M are secured Ybers ti and 53. The rings 52 and 53 also serve to hold the polarizingcoils 48 in place as can be seen from Fig. 6. The two ends of thecylindrical structure are closed by cover plates 54 and 55 which areheld in place by the bolts 56 which also serve to hold the rings 52 and53 in place against the end flanges 51 which may be formed at theextremities of the flanged portions d3. of the member ti. In assemblingthe unit the coils M are positioned within the cylinder il, then themembers it are inserted and fastened by,

the screws $5. The rings 52 and 53 are then put into place and themembers 50 carrying the tral portion of the oscillator where it will besub jected to intense compressional wave vibration...

The space between the pipe 88 and the tine surface 12 is filledwith acompre'ssionalwava' conducting H uii'Such as water-or oil, which may beintroduced by removing the plug 90. The, 3 operation of this deviceissimilar to that of the modifications previously discussed. In thismodification also, however. it may be desirable to slotthe radiatingsurface 12 as shown, for exampley at 9|.

alternating current coils 69 are placed in position The entire unitmay,.

- The reeds in the various arrangements described above may be vibratedby means of piezoelectric crystals instead of electromagnetically.Suitable arrangements of this kind are shown and claimed in my copendingapplication -Serial No. 333,158, filed May 3, 1940. As there shown thecrystals may. for example, be cemented on one surface of the reeds witha vibrational axis parallel to the .reedsurface so that vibraa jacentreeds and in whichthe alternating current coils M are positioned bringsabout a reaction with the alternating held of these coils so that thereeds t'l are set into :dexural vibration which is transmittedandconverted into vibrationtions are transferred between reeds andcrystals by shearing action. I r

Having now described my invention, I claim:

An electroacoustic transducer comprising a radiating plate, meansforming therewith a plu-.

vrality of longitudinal vibrators, said vibrators i being positionedside'by side and having flexurally vibratable reeds extendingtransversely oi the members M and it in a radial direction so thatcompressional waves are transmitted ironrtheentire external surface orthe cylinder in all directions. It theheight or the cylinder ti be madelarge compared with the wave length oi. compressional waves in thesignaling medium at the signaling frequency, the radiation will beconcentrated in a plane perpendicular to the axis 1 oi the unit. Ifdesired, the external surface ofportunity to cooperate with thelongitudinal bar ,acrews it which may be made watertight by thetorindividual motion or each section, and it tends also to permit a largertree amplitude of the radiating suriaca.

. The further modification of my invention which is shown in Figs. 7 and8 is the reverse. of that shown in Figs. .5 and 6 lnthat the radiationof compressional wave energy is directed toward therefrom, the reeds onadjacent vibrators being positioned opposite each other with a smallspace between them, electromagnetic coil" means for'magnetizin saidvibrators in alternate pothe cylinder it may be slotted between adjacentv members M as, indicated at at. This will give;

" the material betweenthefslotted sections an oplarity and therebyestablishing a magnetic field across said space between opposite reedsand coil'means positioned within said space.

2. An electroacoustic transducer comprising a radiating plate, meansforming therewith a pin-- rality' of longitudinal vibrators, saidvibrators being positioned side by side and having flexurelly'vibratable reeds. extending transversely therefrom, the reeds onadjacent vibrators being pos'itioned oppositeeach other with asmall.space between themyelectromagnetic coil means for magnetizing saidvibrators in alternate polarityand thereby establishing a magnetic heldacross said space between opposite reeds, means for the central axis ofthe unit w'here'itmay be ap-' plied to the treatment of liquids or othersub-y radiating surfacelZ has mounted on its external surface aplurality oi vibrators It by means. of

stances. Here the internal cylinder it having a -3. An electroacoustictransducer suppressing magnetic leakage from the vpoles formed by saidvibrators and coil means positioned within said space. I

comprising a radiating plate,-means forming therewith a plurality oflongitudinal vibrators, said vibrators be ing positioned side by sideand'having -fiexur- J ally vibratable reeds extending transverselytherefrom, the reeds on adjacent vibrators belead washers it. Theelements it as in the other 4 ,modiflcations are provided with reeds Hwhich are magnetized with the aid oi the direct current "porizimr coilsill. in the air gaps between ad. iacent reeds there are mountedalternating current coils it supported on U-shaped non-ma ianetic metalchannels to which are fastened by the its ti to reverse iflances t2 and83 extendirom the narrow hanged portions it of the member ill; Theinterior or the unit is closed by the cover plates til and to winch arealso bolted to the ring 82 by the bolts t t, gaskets 81 beinn interposedto make the joint watertight. A

centrally located pipe it which may be made integral with one of thecover plates. ii desired, for

example, the cover plate it, is fitted into an nerture in the othercover plate M by me of a watertight gland 89. This i e a. i! vneedto iormagnetizing said vibrators in alternate po-' lug positioned oppositeeach other with a small space between them, electromagnetic coil meansma and thereby establishing a magnetic field across said space betweenopposite reeds; means including a plurality ofqpermanent' magnetspositioned .to oppose magnetic leakage fromthe poles formed by saidvibrators and coil means positioned within said space.

4. An electroacoustic transducer comprisinga radiating platehaving-formed thereon a plurality of elements elongated ina dimensionpar-,

allel to the surface of said plate and longitudinally vibratable indirections perpendicular to said plate, said elements having elongatedflexurally vibratable reeds extending transversely therefrom andmeansfor vibrating Said reedSJ 5. An electroacoustic transducercomprising a, radiatingplatahavinsnrormed thereon a plu-f acre,

rality of elements longitudinally vibratable in directions perpendicularto said plate, said elements positioned side by side and havingflexrections substantially perpendicular to the axisof said cylinder,said elements-having flexurally vibratable reeds extending transverselytherefrom and means for vibrating said reeds.

'7. An ele'ctroacoustic transducer comprising a cylindrical radiatingmember, means forming therewith a plurality of vibrators adapted tovibrate in directions substantially perpendicular to the axis of saidcylinder at a predetermined natural frequency, said vibrators havingflexurally vibratable reeds extending transversely therefrom and havinga natural frequency of vibration corresponding to that of said vibratorsand means for vibrating said reeds.

ti. An electroacoustic transducer comprising a cylindrical radiatingmember having formed thereon a plurality of elements vibratable indirection substantially perpendicular to the axis oi said cylinder, saidelements being positioned side by side and having flexurally vibratablereeds extending transversely therefrom, the reeds on adjacent elementsbein positioned opposite each other with a small'space between them,means providing a magnetic field across said space from one reed to theopposite reed and coil means positioned within said space,

a. an electroacoustic transducer comprising a cylindrical radiatingmember having an external rziidiating surface and having formed on itsinternal surface a plurality of elements vibratable in directionssubstantially perpendicular to'the axis of said cylinder, said elementsbeing positioned side by said and having fiexurally vibratable rcedsextending transversely therefrom, the reeds on adjacent elements beingpositioned opposite each other with a small space between them, meansproviding a magnetic field across said space from one reed to theopposite reed and coil means positioned within said space. V

10. An clectroacoustic transducer comprising a cylindrical radiatingmember havin an internal radiating surface and having formed on itsexternal surf ace a plurality of elements vibratable in directionssubstantially perpendicular to the axis of said cylinder, said elementsbeing positioned side by side and having fiexurally vibratable reedsextending transversely therefrom, the reeds on adjacent elements beingpositioned opposite each other with a small space between them, meansproviding a magnetic field across said space from onereed to theopposite reed and coil means positioned within said space.

11. An. electroacoustic device for treating liquids with compressionalwaves comprising 9. cy lindrical radiating member having an internalradiating surface and having formed on its ex ternal surface a pluralityof elements vibratable in directions substantially perpendicular to theaxis of said cylinder, said elements being positioned side by side andhaving flexurally vibratable reeds extending transversely therefrom, thereeds on adjacent elements being positioned opposite each other with asmall space between coil means positioned within said space, meansclosing the space within said cylindrical member, and means forconducting liquids to be treated along the axis of said cylinder.

12. An electroacoustic transducer comprising a radiating member, meansincluding said member forming a plurality of half wave length vibrators,each of said vibrators being composed of said radiating member with alongitudinally vibrating element extending therefromhaving a free endand a node intermediate of the ends of the means taken longitudinally,means including a, plurality of reeds extending normally from saidlongitudinally vibrating elements at points in the vicinity oftheir'free ends, said reeds being adapted to vibrate fiexurally at thefrequency corresponding to said half wave length for'vibrating saidvibrator and means for vibrating said reeds.

13. An electroacoustic transducer comprising a radiating member, meansincluding said, member forming a half wave length vibrator, saidvibrator being composed of said radiating member with a longitudinallyvibrating element extending therefrom'having a, free end and having anode intermediate of the ends of the means taken longitudinally, meansincluding a reed extending normally from said longitudinally vibratingelement at a point in the vicinity of the free end of the reed, saidreed being adapted to vibrate fiexurally at a frequency corresponding tosaid half wave length for .vibrating said vibrator and means forvibrating said reed.

14. An electroacoustic transducer comprising a plurality of half wavelength'longitudinally vibratable units, each composed of a. radiatingelement joined with a longitudinally vibrating element forming togethercombined elements each ha ing a node between the ends of a combinedelement, said units being arranged side by side, and means for vibratingsaid elements including vibratory reeds formed integrally with saidlongitudinally vibrating elements on both sides thereof and extendingperpendicularly from said sides, the reeds on adjacent elements beingopposite to each other with an air gap between them and said reedshaving length and thickness dimensions to give eachof them a naturalfrequency of vibration equal to theirequencyof which 'said elements area half wave length, means providing a magnetic flux across said air gapsand coil means positioned in said air gaps.

15. An electroacoustic transducer comprising a radiating member, meansforming therewith a plurality of half wave length vibrators, each ofsaid vibrators being composed of said radiating member with alongitudinally vibrating element having a node intermediate of the endsof the meanstaken longitudinally, said longitudinally vibrating elementshaving flexurally vibratable reeds extending normally from the sides ofsaid longitudinally vibrating elements near their ends and means, forvibrating said reeds.

16. An electroacoustic transducer comprising a radiating member, meansforming therewith a plurality of longitudinal vibrators, each of saidvibrators being composed of said radiating member with a longitudinallyvibrating element having a node intermediate of the ends of the meanstaken longitudinally, each of said vibrators having a natural frequencyof vibration, said longitudinally vibrating elements of said vibratorshaving flexurally vibratable reeds extending normally from the sides ofsaid longitudinal vibrators ."iear their ends, said reeds having thesame iatural frequency of vibration as said vibrators and means forvibrating said reeds.

17. An electroacoustic transducer comprising a radiating member, meansforming therewith a. ongitudinal vibrator, said vibrator being com-JOSGd of said radiating member with a longituiinally vibrating elementhavinga node internediate of the ends of the means taken longituiinally,said vibrator having a natural frequency if vibration and havingfiexurally vibratable 'eeds extending normally from the sides of saidongitudinally vibrating element near their ends, :aid reeds having thesame natural frequency of ibration as said vibrator and means forvibratng the said reeds.

HUGO BEN'IOFF.

REFERENCES CITED The following references are of record in the file ofthis patent:

